The purpose of this project is to determine the chemical nature of the catalytically active centers of 3-phosphoglyceraldehyde dehydrogenase and to relate these structures to the various activities of the enzyme in vivo and in vitro. Six types of reactions are catalyzed by the enzyme; dehydrogenase, transacetylase, phosphatase, esterase, diaphorase, and transphosphorylase. Four reactive amino acid residues have been specifically identified and their functions in the catalytic reactions have been elucidated. We propose to prepare additional enzyme complexes with substrates, coenzymes, and inhibitors in order to identify additional active sites involved in the various activities of the enzyme. These studies will be correlated with the more detailed crystallographic analysis which is currently in progress. The data on the structure and catalytic mechanism will be extrapolated to an investigation of the functioning of the enzyme in the muscle cell. For example, this dehydrogenase is inhibited by ATP and phosphocreatine which occur in muscle at very high concentrations. The mechanism of this inhibition and its relationship to the contractile process will be further investigated. An attempt will be made to relate the findings to the metabolic disorders of muscular dystrophy.